Process for producing a flexographic printing plate

ABSTRACT

A developing solution comprising (A) at least one aromatic hydrocarbon having a boiling point of from 150° to 300° C.; (B) at least one alcohol represented by the following formula (I): 
     
         R.sup.1 OH                                                 (I) 
    
     wherein R 1  represents an aliphatic or alicyclic alkyl group having from 5 to 12 carbon atoms, --C n  H 2n  Ar, --(C m  H 2m  O) p  C q  H 2q+1 , a furfuryl group or a hydrogenated furfuryl group, an alkyl group substituted by an acyl group or an epoxy group, or --CH 2  CH 2  (OCH 2  CH 2 ) r  OR 2  ; in which Ar represents an aromatic group; n represents an integer of from 1 to 3; m represents an integer of from 2 to 6; p represents 1 or 2; q represents 0 or an integer of from 1 to 4; R 2  represents a hydrogen atom or an alkyl group; and r represents 0, 1 or 2; and (C) at least one compound represented by the following formula (II): ##STR1## wherein R 3  and R 4  are the same or different and each represents an alkyl group having from 3 to 6 carbon atoms; the proportions of components (A), (B), and (C) being from 25 to 70% by weight, from 20 to 50% by weight, and from 0.001 to 40% by weight, respectively, each based on the sum of components (A), (B), and (C).

This is a divisional of application No. 08/265,338 filed Jun. 24, 1994,now U.S. Pat. No. 5,521,054, issued May 28, 1996.

FIELD OF THE INVENTION

This invention relates to a developing solution to be used for formationof a relief comprising a photosensitive resin composition, and moreparticularly to a developing solution suitable for making a flexographicprinting plate having excellent dimensional stability and resolutionirrespective of its thickness.

BACKGROUND OF THE INVENTION

Known photosensitive resin compositions for flexographic printing plateinclude compositions comprising a thermoplastic elastomer, aphotopolymerizable unsaturated monomer, and a photopolymerizationinitiator, such as those described in JP-B-51-43374 and JP-B-59-22219(the term "JP-B" as used herein means an "examined Japanese patentpublication"). The photosensitive resin composition is exposed to activelight rays through a mask having a prescribed pattern, and the unexposedarea is washed away with a developing solution. Since the photosensitivelayer comprises, for example, a hydrophilic thermoplastic elastomer, thephotosensitive resin layer does not dissolve in water or an aqueoussolvent so that chlorine organic solvents, such as chloroform,trichloroethane, trichloroethylene, and tetrachloroethylene, have beenused as a developing solution.

Although the chlorine organic solvents are stable and easy to handle onaccount of their nonflammability, they not only involve health problemsbecause of their high toxicity but also form one of the causes ofdestruction of the ozonosphere and are therefore unfavorable from thestandpoint of working environment and environmental protection such asair pollution. For these reasons, it has been demanded to develop anon-chlorine developing solution. To this effect, a developing solutioncomprising an aromatic hydrocarbon and a paraffin or naphthenehydrocarbon at a specific volume ratio (see JP-A-5-134416, the term"JP-A" as used herein means an "unexamined published Japanese patentapplication") and an organic solvent system comprising a specific esterand an alcohol at a specific volume ratio (see JP-A-4-18564) have beenproposed.

The developing solutions according to JP-A-3-322416 are less causativeof health and environmental problems than the conventional chlorineorganic solvents. However, besides giving off an unpleasant smell, theytend to swell the image area during the development, resulting in afailure of obtaining good image reproduction unless their composition isaltered according to the thickness of the plate. Since the developingsolution according to JP-A-4-18564 comprises a specific ester, it isexpensive and cannot be supplied in large quantity at a low price.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a developing solutionfor producing a flexographic printing plate, which is free from thedisadvantages associated with the conventional developing solutions,i.e., a developing solution which is easy to handle and provides animage area with high resolution (e.g., free from missing of fine lines,small points, small types) and high dimensional stability irrespectiveof the thickness of the plate.

As a result of extensive studies, the inventors have now found that thisand other objects of the present invention are accomplished by adeveloping solution comprising a specific aromatic hydrocarbon, analcohol, and a compound represented by formula (II) shown below in aspecific volume ratio and thus completed the present invention.

The present invention provides a developing solution comprising

(A) at least one aromatic hydrocarbon having a boiling point of from150° to 300° C.;

(B) at least one alcohol represented by the following formula (I):

    R.sup.1 OH                                                 (I)

wherein R¹ represents an aliphatic or alicyclic alkyl group having from5 to 12 carbon atoms, --C_(n) H_(2n) Ar, --(C_(m) H_(2m) O)_(p) C_(q)H_(2q+1), a furfuryl group or a hydrogenated furfuryl group, an alkylgroup substituted by an acyl group or an epoxy group, or --CH₂ CH₂ (OCH₂CH₂)_(r) OR² ; in which Ar represents an aromatic group; n represents aninteger of from 1 to 3; m represents an integer of from 2 to 6; prepresents 1 or 2; q represents 0 or an integer of from 1 to 4; R²represents a hydrogen atom or an alkyl group; and r represents 0, 1 or2; and

(C) at least one compound represented by the following formula (II):##STR2## wherein R³ and R⁴ are the same or different and each representsan alkyl group having from 3 to 6 carbon atoms; the proportions ofcomponents (A), (B), and (C) being from 25 to 70% by weight, from 20 to50% by weight, and from 0.001 to 40% by weight, respectively, each basedon the sum of components (A), (B), and (C).

Further, the present invention provides a process for producing aflexographic printing plate comprising the step of washing away aphotosensitive resin composition with the above-described developingsolution.

DETAILED DESCRIPTION OF THE INVENTION

The photosensitive resin composition to which the present inventionapplies mainly comprises a thermoplastic elastomer, a photopolymerizableunsaturated monomer, and a photopolymerization initiator.

The thermoplastic elastomer is a high polymer (high molecular compound)which assumes rubber-like elasticity like vulcanized rubber at ambienttemperature and exhibits thermoplasticity at high temperatures. Examplesof the thermoplastic elastomers include styrene elastomers, olefinelastomers, polyester elastomers, polyurethane elastomers,1,2-polybutadiene elastomers, vinyl chloride elastomers, and polyamideelastomers. Preferred of them are styrene-based thermoplasticelastomers, such as a styrene-butadiene-styrene block copolymer, astyrene-isoprene-styrene block copolymer, and hydrogenation productsthereof. The thermoplastic elastomer is used in an amount of from 30 to95% by weight, preferably from 50 to 85% by weight, based on thephotosensitive resin composition. When the proportion of thethermoplastic elastomer is less than 30% by weight, the composition hasinsufficient rubber-like elasticity. When it exceeds 95% by weight, highreproducibility in pattern formation is hardly obtained.

The photopolymerizable unsaturated monomer is a compound having at leastone addition polymerizable unsaturated bond in the molecule thereof andis not particularly limited as long as it is compatible with theabove-mentioned thermoplastic elastomer. Examples of usablephotopolymerizable unsaturated monomers include acrylic esters,acrylamide and its derivatives, methacrylic esters, methacrylamide andits derivatives, allyl compounds, vinyl ethers, vinyl esters, styreneand its derivatives, and crotonic esters. Alcohols which can be used inthe preparation of the ester monomers just referred to include aliphaticor alicyclic diols having from 2 to 10, and preferably from 2 to 6,carbon atoms, such as ethylene glycol, triethylene glycol, hexanediol,and cyclohexanediol. These photopolymerizable unsaturated monomers maybe used either individually or in combination of two or more thereof.The photopolymerizable unsaturated monomers are used in an amount offrom 3 to 80 parts by weight, preferably from 5 to 20 parts by weight,per 100 parts by weight of the thermoplastic elastomer. When theproportion of the monomers is less than 3 parts by weight, highreproducibility in pattern formation is hardly obtained. When it exceeds80 parts by weight, satisfactory rubber-like elasticity cannot beobtained.

The photopolymerization initiator is arbitrarily selected from commonlyemployed ones. Benzoin photopolymerization initiators, benzophenonephotopolymerization initiators and anthraquinone photopolymerizationinitiators are preferred. The photopolymerization initiators may be usedeither individually or in combination of two or more thereof. Theinitiators are used in an amount of from 0.1 to 5 parts by weight,preferably from 0.5 to 2 parts by weight, per 100 parts by weight of thethermoplastic elastomer. When the proportion of the initiator is lessthan 0.1 part, practical sensitivity cannot be obtained. When it exceeds5 parts, a satisfactory pattern cannot be formed.

If desired, the photosensitive resin composition may contain additivesfor improving various properties, such as dyes, pigments, polymerizationinhibitors, antioxidants, and light deterioration inhibitors. In orderto improve abrasion resistance, the composition may further containother resins compatible with the thermoplastic elastomer, such aspolyamide resins, epoxy resins, and polyurethane resins.

The photosensitive resin layer for flexographic printing plateproduction is formed by a known method. For example, a thermoplasticelastomer, a photopolymerizable unsaturated monomer, aphotopolymerization initiator and other necessary additives aredissolved in an appropriate organic solvent to prepare a coatingcomposition, the coating composition is shaped into a film or a plate,and the solvent is removed. Alternatively, the above components aremixed in a roll mixer and molded into a film or a plate by means of ahot press.

The photosensitive resin layer preferably has a thickness of from 1 to 8mm. When it is used for a corrugated fiberboard, the thickness thereofis preferably from 4 to 8 mm. When it is used for other materials, thethickness thereof is preferably from 1 to 4 mm.

In order to prevent desensitization by oxygen in air or blocking, awater-soluble or alcohol-soluble resin, such as cellulose derivatives,polyamide resins or polyimide resins, (hereinafter referred to as ananti-tack resin) is applied on the photosensitive resin layer to form ananti-tack resin layer having a thickness of from 1 to 10 μm.

The photosensitive resin layer is press bonded to a plate such as apolyester sheet, a steel plate and an aluminum plate, and imagewiseexposed to active light rays through a mask. The unexposed area is thenremoved usually by brushing in a developing solution or by applying aspray of a developing solution to obtain a rubbery relief plate forflexographic printing.

The developing solution according to the present invention is a mixturecomprising the above-described components (A), (B), and (C).

The aromatic hydrocarbon as component (A) has a property of easilydissolving or swelling the photosensitive resin layer. Component (A) isused in a proportion of from 25 to 70% by weight, preferably from 40 to60% by weight. When the proportion of component (A) is less than 25% byweight, the rate of development becomes low, and washing away of thephotosensitive resin layer takes time. When it exceeds 70% by weight,the developing solution excessively swells the photosensitive resinlayer and is incapable of dissolving the anti-tack resin layer. From theviewpoint of non-flammability and ease of drying, the aromatichydrocarbon as component (A) should have a boiling point of from 150° to300° C, preferably from 180° to 250° C. Those having a boiling point oflower than 150° C. considerably vaporize into easily ignitable vapors inthe air. Those having a boiling point exceeding 300° C. are lessvaporizable and less ignitable and therefore less dangerous but need anunfavorably prolonged drying time.

Specific examples of the aromatic hydrocarbons suitable as component (A)include diethylbenzene, propylbenzene, isopropylbenzene, amylbenzene,diamylbenzene, amyltoluene, cymene, and a mixture thereof (e.g., crudeoil, naphtha obtained by dry distillation of coal). These aromatichydrocarbons may be used either individually or in combination of two ormore thereof. The mixture of aromatic hydrocarbons noted above arecommercially available under trade names of Solvesso 100, Solvesso 150and Solvesso 200 (products of Exxon Chemical Japan Limited) and Swazol100, Swazol 200, Swazol 310, Swazol 1000, Swazol 1500 and Swazol 1800(products of Maruzen Petrochemical Company Limited). Component (A) maycontain one or more additives such as benzene, toluene, xylene,ethylbenzene, triamylbenzene, tetraamylbenzene, dodecylbenzene anddidodecylbenzene to such a degree that does not lower the ignitionpoint. The components of the above-described mixtures of aromatichydrocarbons are shown in Table 1 below.

                  TABLE 1                                                         ______________________________________                                                                      Boiling                                                                       Point                                           Trade Name                                                                             Components           (°C.)                                    ______________________________________                                        Solvesso 100                                                                           Methylethylbenzene,  164-176                                                  Trimethylbenzene,                                                             Diethylbenzene,                                                               Dimethylethylbenzene                                                 Solvesso 150                                                                           Unknown              188-209                                         Solvesso 200                                                                           Methylnaphthalene,   231-275                                                  Dimethylnaphthalene,                                                          Diphenylnaphthalene,                                                          C.sub.11 aromatics                                                   Swazol 100                                                                             Octane, Nonane, Toluene                                                                            103-124                                         Swazol 200                                                                             Nonane, Alkane(C = 10-29),                                                                         131-150                                         Swazol 310                                                                             Alkane(C = 10-29),   153.5-179                                                Tri- or tetramethylbenzene,                                                   Alkyl(C = 2-4)toluene                                                         Branched alkyl(C = 3-36)benzene                                      Swazol 1000                                                                            Tri- or tetramethylbenzene,                                                                        161-179                                                  Alkyl(C = 2-4)toluene,                                                        Branched alkyl(C = 3-36)benzene                                      Swazol 1500                                                                            Tri- or tetramethylbenzene,                                                                        180.5-208.5                                              Cymene, Diethylbenzene,                                                       Naphthalene                                                          Swazol 1800                                                                            Diethylbenzene,      195.5-245                                                Branched alkyl(C = 3-36)benzene,                                              Mono- and dimethylnaphthalene,                                                Naphthalene                                                          ______________________________________                                         *Note: C means a carbon number.                                          

The alcohol as component (B) is capable of dissolving an anti-tack resinlayer and hardly capable or incapable of dissolving a photosensitiveresin layer, rather acting against swelling of the photosensitive resinlayer with component (A). Component (B) is used in a proportion of from20 to 50% by weight, preferably from 30 to 40% by weight. When theproportion of component (B) is less than 20% by weight, the developingsolution is incapable of dissolving an anti-tack resin layer. When itexceeds 50% by weight, the developing solution exerts excessiveinhibitory action on swelling and needs much time for development.

In formula (I), the aliphatic alkyl group represented by R¹ may have astraight-chain or branched structure. The alkyl moiety of the alicyclicalkyl group represented by R¹ may also have a straight-chain or branchedstructure.

Examples of the alcohol represented by formula (I), wherein R¹ is analiphatic or alicyclic alkyl group, include n-amyl alcohol, isoamylalcohol, sec-amyl alcohol, 3-pentanol, tert-amyl alcohol, hexanol,2-ethylhexanol, methylamyl alcohol, 2-ethylbutanol, 2-heptanol,3-heptanol, n-octanol, 2-octanol, 2-ethylhexanol,3,5,5-trimethylhexanol, nonanol, decanol, undecanol, dodecanol,cyclohexanol and methylcyclohexanol.

Examples of the alcohol represented by formula (I), wherein R¹ is--C_(n) H_(2n) --Ar (wherein Ar is an aromatic group; and n is 1 to 3),include 2-phenylethanol and benzyl alcohol.

When R¹ in formula (I) is --(C_(m) H_(2m) O)_(p) C_(q) H_(2q+1) (whereinm is 2 to 6; p is 1 or 2; and q is 0 to 4), the alkylene moiety --C_(m)H_(2m) -- and the alkyl moiety --C_(q) H_(2q+1) may have astraight-chain, branched or cyclic structure. Examples of the alcoholrepresented by formula (I), wherein R¹ is --(C_(m) H_(2m) O)_(p) C_(q)H_(2q+1), include 3-methoxybutanol, 2-butoxyethanol,3-methoxy-3-methylbutanol and 4-(4'-methoxybutoxy)butanol.

Examples of the alcohol represented by formula (I), wherein R¹ is afurfuryl group or a hydrogenated furfuryl group, include furfurylalcohol and tetrahydrofurfuryl alcohol.

Examples of the alcohol represented by formula (I), wherein R¹ is analkyl group substituted by an acyl group or an epoxy group, includediacetone alcohol and glycidol.

Examples of the alcohol represented by formula (I), wherein R¹ is --CH₂CH₂ (OCH₂ CH₂)_(r) OR² (wherein R² represents a hydrogen atom or analkyl group; and r is 0, 1 or 2), include ethylene glycol and monoalkylethers thereof, diethylene glycol and monoalkyl ethers thereof, andtriethylene glycol and monoalkyl ethers thereof.

Among these alcohols, preferred is 3-methoxy-3-methylbutanol.

The compound represented by formula (II) as component (C) has an aromaand is capable of mildly removing the unexposed area of a photosensitiveresin layer. Accordingly, component (C) controls the swelling action ofcomponent (A) on the exposed area without reducing the developingability of the developing solution and thereby contributes to highresolution such as development of fine lines, small points and smalltypes. Additionally, component (C) disguises the unpleasant smell ofcomponent (A). Component (C) is used in a proportion of from 0.001 to40% by weight, preferably from 0.1 to 25% by weight. When the proportionof component (C) is less than 0.001%, no effect on swelling control orsmell control is produced. When it exceeds 40%, the excessive inhibitoryeffect on swelling is exerted to retard the development. As a result,the exposed area cannot be prevented from being swollen with component(A). Such a high proportion is also uneconomical.

In formula (II), the alkyl groups represented by R³ and R⁴ may have astraight-chain, branched or cyclic structure. Of the compoundsrepresented by formula (II), the compounds, wherein at least one of R³and R⁴ is a branched alkyl group are preferred for their great effect oninhibition of swelling. Examples of such compounds include n-butylisobutyrate, isobutyl n-butyrate, isobutyl isobutyrate, isobutyl2-methylbutyrate, and isobutyl 3-methylbutyrate, with isobutylisobutyrate being more preferred.

The developing solution according to the present invention may containone or more additives such as solvents in an amount of from 0 to 35% byweight based on the total weight of the developing solution, ascomponent (D). Examples of the solvents include naphthene hydrocarbonsand paraffin hydrocarbons.

The developing solution according to the present invention exhibits theaction of inhibiting swelling and the action of masking the unpleasantsmell of an aromatic hydrocarbon, which are attributed to component (C),and the action of controlling swelling, which is attributed to component(B), in good balance. Thus, the developing solution achieves developmentat a high resolution while inhibiting the swelling of the exposed areato provide a flexographic printing plate with high line width accuracyirrespective of the thickness of the plate. Containing no chlorinecomponent, the developing solution favors environmental sanitation andprotection. Having a high boiling point, the developing solution has ahigh ignition point and is very safe on use.

The present invention will now be illustrated in greater detail by wayof the following examples, but it should be understood that the presentinvention is not to be construed as being limited thereto. All thepercents and parts are by weight unless otherwise indicated.

EXAMPLE 1

In 200 parts of methyl ethyl ketone were dissolved 100 parts of astyrene-butadiene-styrene block copolymer (TRKX65S, a product of ShellKagaku K.K.; weight average molecular weight: 130,000; styrene unitcontent: 28%), 60 parts of liquid polybutadiene (NISSO-PB B-1000, aproduct of Nippon Soda Co., Ltd.; weight average molecular weight: 1050;1,2-vinyl content: 85% or more), 6 parts of trimethylolpropanetriacrylate, 2 parts of benzyl dimethyl ketal, and 0.012 part of2,6-di-tert-butyl-p-cresol in a flask while stirring under reflux forabout 2 hours. The resulting photosensitive resin composition wasapplied to a 100 μm thick polyethylene terephthalate (PET) film(substrate) having thereon an adhesive layer to obtain a photosensitiveresin plate having a dry photosensitive resin layer thickness of 2.74 mmand dried at 60° C. for 12 hours.

Separately, a composition consisting of 100 g of methanol and 5 g of analcohol-soluble polyamide (Macromelt 6900, a product of HenckelCorporation) was applied to a 100 μm thick PET film as a temporarysubstrate and dried at 60° C. for 2 minutes to form a polyamide coatedlayer (an anti-tack resin layer) having a thickness of 5 μm. Thepolyamide coated layer was adhered to the above-prepared photosensitiveresin layer via an adhesive.

Active light rays of a chemical lamp (FL-40BL manufactured by ToshibaCorporation) was applied to the entire surface from the substrate sidefor 2 minutes. The PET film of the polyamide coated layer side wasstripped off, and a negative film having a parallel line pattern havinga line width of 0.1 mm was brought into contact with the photosensitiveresin layer under reduced pressure. The photosensitive resin layer wasselectively irradiated with active light rays for 15 minutes using thesame chemical lamp.

A developing solution was prepared from 4 kg of Solvesso 150 (anaromatic hydrocarbon solvent produced by Exxon Chemical Japan Limited;boiling point (b.p.): 188°-209° C.), 3.25 kg of benzyl alcohol, and 0.75kg of isobutyl isobutyrate. The unexposed area of the photosensitiveresin layer were removed with the developing solution in a brushdeveloping machine at 25° C. for 2 minutes. After drying at 50° C. for30 minutes, the entire surface of the plate was irradiated using thesame chemical lamp for 15 minutes to obtain a flexographic printingplate, in which the line width of 0.1 mm was accurately reproduced.

EXAMPLE 2

A flexographic printing plate was prepared in the same manner as inExample 1, except for using a developing solution consisting of 4.8 kgof Swazol 1500 (an aromatic hydrocarbon solvent produced by MaruzenPetrochemical Company Limited; b.p.: 180.5°-208.5° C.), 3.184 kg ofbenzyl alcohol, and 0.016 kg of isobutyl isobutyrate. The developingsolution gave off a reduced petroleum smell of Swazol. The line width of0.1 mm was accurately reproduced in the resulting flexographic printingplate.

COMPARATIVE EXAMPLE 1

A flexographic printing plate was prepared in the same manner as inExample 2, except for using a developing solution consisting of 6 kg ofSwazol 1500 and 4 kg of benzyl alcohol. The smell of the developingsolution was too strong for the worker to continue developmentprocessing for a long time. The resulting flexographic printing platesuffered from partial waviness of the line pattern.

COMPARATIVE EXAMPLE 2

A flexographic printing plate was prepared in the same manner as inExample 2, except for using a developing solution consisting of 6 kg ofSwazol 1500 and 2 kg of isobutyl isobutyrate. The anti-tack resin layerof the flexographic printing plate was not completely removed, resultingin uneven development.

COMPARATIVE EXAMPLE 3

A flexographic printing plate was prepared in the same manner as inExample 2, except for using a developing solution consisting of 1.6 kgof Swazol 1500, 2.4 kg of benzyl alcohol, and 4 kg of isobutylisobutyrate. Two minutes' development processing was insufficient forreproduction of the pattern so that the processing was further continuedfor an additional period of 1 minute. The resulting flexographicprinting plate suffered from partial waviness of the line pattern.

EXAMPLE 3

The same photosensitive resin composition as prepared in Example 1 wasapplied to each of a PET film having thereon an adhesive layer(substrate) and a PET film with no adhesive, both having a thickness of100 μm, to a dry thickness of 3.0 mm and 3.25 mm, respectively, anddried at 60° C. for 1 hour. The two coated films were laminated withtheir photosensitive resin layers facing to each other, and the laminatewas further dried at 60° C. for 1 hour. The PET film with no adhesivewas stripped off, an adhesive was applied to the thus exposedphotosensitive resin layer, and the same polyamide coated resin layerformed on a 100 μm thick PET film as prepared in Example 1 was laminatedthereon to obtain a photosensitive resin plate having a dryphotosensitive resin layer thickness of 6.25 mm.

Active light rays of a chemical lamp (FL-40BL) was applied to the entiresurface of the laminate from the substrate side for 4 minutes. The PETfilm of the polyamide coated layer side was stripped off, and a negativefilm having a parallel line pattern having a line width of 0.2 mm wasbrought into contact with the photosensitive resin layer under reducedpressure. The photosensitive resin layer was selectively irradiated withactive light rays for 15 minutes using the same chemical lamp throughthe negative film.

The unexposed area of the photosensitive resin layer were removed withthe same developing solution as prepared in Example 1 at 25° C. for 5minutes. After drying at 50° C. for 40 minutes, the entire surface ofthe plate was irradiated using the same chemical lamp to obtain aflexographic printing plate, in which the relief depth was 2.5 mm andthe line width of 0.2 mm was accurately reproduced.

EXAMPLE 4

A photosensitive resin plate was prepared in the same manner as inExample 1, except for increasing the thickness of the photosensitiveresin layer to 6.25 mm. After imagewise exposure in the same manner asin Example 3, the photosensitive resin layer was developed with the samedeveloping solution as used in Example 2 at 25° C. for 5 minutes, driedat 50° C. for 40 minutes, and irradiated overall with light using thesame chemical lamp as used in the foregoing Examples. The line width of0.2 mm was accurately reproduced in the resulting flexographic printingplate.

COMPARATIVE EXAMPLE 4

A flexographic printing plate was prepared in the same manner as inExample 4, except for using the same developing solution as used inComparative Example 1. The resulting flexographic printing plate gaveoff a petroleum smell and suffered from partial wariness of the 0.2 mmwide lines.

COMPARATIVE EXAMPLE 5

A flexographic printing plate was prepared in the same manner as inExample 4, except for using the same developing solution as used inComparative Example 2. The anti-tack resin layer of the flexographicprinting plate was not completely removed for 5 minutes' developmentprocessing, and for further 3 minutes' development processing.

COMPARATIVE EXAMPLE 6

A flexographic printing plate was prepared in the same manner as inExample 4, except for using the same developing solution as used inComparative Example 3. Seven minutes' development processing wasrequired for obtaining the relief depth of 2.5 mm, and the 0.2 mm widelines have a partial waviness.

EXAMPLE 5

A flexographic printing plate was prepared in the same manner as inExample 1, except for using a developing solution consisting of 3.2 kgof Solvesso 150, 1.8 kg of 3-methoxy-3-methylbutanol, 0.4 kg of isobutylisobutyrate and 2.6 kg of Naphthezole L (a naphthalene solventmanufactured by Nippon Petrochemicals Co., Ltd.; b.p.: 177°-200° C.).The line width of 0.1 mm was accurately reproduced in the resultingflexographic printing plate.

The results obtained in Examples 1 to 5 and Comparative Examples 1 to 6are shown in Table 1 below.

In Table 1, "good" in "reproducibility of line image" means that, whenthe plate has a thickness of 2.84 mm, the line width of 0.1 mm wasaccurately reproduced, and that, when the plate has a thickness of 6.35mm, the line width of 0.2 mm was accurately reproduced. "poor" thereinmeans that they were not achieved.

"good" in "developing time" means that, when the plate has a thicknessof 2.84 mm, development was achieved within 2 minutes, and that, whenthe plate has a thickness of 6.25 mm, development was achieved within 5minutes. "poor" therein means that they were not achieved within 2 and 5minutes, respectively.

A developing solution which had a weak smell and completely dissolvedthe anti-tack resin layer and the unexposed area of the photosensitiveresin layer within prescribed minutes to provide a flexographic printingplate on which a line pattern was accurately reproduced was rated"good". When not, the developing solution was rated "poor".

                                      TABLE 2                                     __________________________________________________________________________           Composition of  Plate   Dissolving                                                                           Reproduci-                                     Developing Solution                                                                           Thick-  Power for                                                                            bility                                  Example                                                                              (A) (B) (C) (D) ness*   Anti-tack                                                                            of Line                                                                             Developing                                                                          Total                       No.    (wt %)                                                                            (wt %)                                                                            (wt %)                                                                            (wt %)                                                                            (mm)                                                                              Smell                                                                             Resin Layer                                                                          Image Time  Judgement                   __________________________________________________________________________    Example 1                                                                            50  40.6                                                                              9.4 --  2.84                                                                              weak                                                                              good   good  good  good                        Example 2                                                                            60  39.8                                                                              0.2 --  2.84                                                                              weak                                                                              good   good  good  good                        Comparative                                                                          60  40  --  --  2.84                                                                              strong                                                                            good   poor  good  poor                        Example 1                                                                     Comparative                                                                          75  --  25  --  2.84                                                                              weak                                                                              poor   poor  poor  poor                        Example 2                                                                     Comparative                                                                          20  30  50  --  2.84                                                                              weak                                                                              good   poor  poor  poor                        Example 3                                                                     Example 3                                                                            50  40.6                                                                              9.4 --  6.35                                                                              weak                                                                              good   good  good  good                        Example 4                                                                            60  39.8                                                                              0.2 --  6.35                                                                              weak                                                                              good   good  good  good                        Comparative                                                                          60  40  --  --  6.35                                                                              strong                                                                            good   poor  good  poor                        Example 4                                                                     Comparative                                                                          75  --  25  --  6.35                                                                              weak                                                                              poor   poor  poor  poor                        Example 5                                                                     Comparative                                                                          20  30  50  --  6.35                                                                              weak                                                                              good   poor  poor  poor                        Example 6                                                                     Example 5                                                                            40  22  5   33  2.84                                                                              weak                                                                              good   good  good  good                        __________________________________________________________________________     Note: *Inclusive of the thickness of the substrate.                      

As is apparent from the results in Table 2, the developing solutionaccording to the present invention has a weak smell and exhibitsexcellent performance in removal of an anti-tack resin layer anddevelopment of a photosensitive resin layer to achieve high resolution.The present invention thus makes it possible to produce, in a reduceddeveloping time, a flexographic printing plate having excellentresolution and dimensional stability irrespective of the platethickness.

While the invention has been described in detail and with reference tospecific examples thereof, it will be apparent to one skilled in the artthat various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

What is claimed is:
 1. A process for producing a flexographic printingplate comprising the steps of image-wise exposing a photosensitive resincomposition on a substrate and then selectively washing away unexposedareas of the photosensitive resin composition with a developing solutionto form a relief pattern of the photosensitive resin composition on thesubstrate, wherein the developing solution consists essentially of:(A)at least one aromatic hydrocarbon having a boiling point of from 150° to300° C.; (B) at least one alcohol represented by the following formula(I):

    R.sup.1 OH                                                 (I)

wherein R¹ represents an aliphatic or alicyclic alkyl group having from5 to 12 carbon atoms, --C_(n) H_(2n) Ar, --(C_(m) H_(2m) O)_(p) C_(q)H_(2q+1), a furfuryl group or a hydrogenated furfuryl group, an alkylgroup substituted by an acyl group or an epoxy group, or "--CH₂ CH₂(OCH₂ CH₂)_(r) OR² "; in which Ar represents an aromatic group; nrepresents an integer of from 1 to 3; m represents an integer of from 2to 6; p represents 1 or 2; q represents 0 or an integer of from 1 to 4;R² represents a hydrogen atom or an alkyl group; and r represents 0, 1or 2; and (C) isobutyl isobutyrate; the proportions of components (A),(B), and (C) being from 25 to 70% by weight, from 20 to 50% by weight,and from 0.001 to 40% by weight, respectively, each based on the sum ofcomponents (A), (B), and (C).
 2. The process as claimed in claim 1,wherein the photosensitive resin composition comprises a thermoplasticelastomer, a photopolymerizable unsaturated monomer, and aphotopolymerization initiator.
 3. The process according to claim 2,wherein component (A) is used in a proportion of from 40 to 60% byweight based on the sum of components (A), (B), and (C).
 4. The processaccording to claim 2, wherein component (B) is used in a proportion offrom 30 to 40% by weight based on the sum of components (A), (B), and(C).
 5. The process according to claim 2, wherein component (C) is usedin a proportion of from 0.1 to 25% by weight based on the sum ofcomponents (A), (B), and (C).